package StackAndQueue;

public class LoopQueue<E> implements Queue<E> {

    private E[] data;
    private int front,tail;
    private int size;

    public LoopQueue(int capacity){
        data = (E[])new Object[capacity + 1];
        front = 0;
        tail = 0;
        size = 0;
    }

    public LoopQueue(){
        this(10);
    }

    public int getCapacity(){
        return data.length - 1;
    }

    @Override
    public int getSize() {
        return size;
    }

    @Override
    public boolean isEmpty() {
        return front == tail;
    }

    @Override
    public void enqueue(E e) {

        if((tail + 1) % data.length == front)  //判断队列是否为满
            resize(getCapacity() * 2);

        data[tail] = e;
        tail = (tail + 1) % data.length;
        size++;
    }

    private void resize(int newCapacity){

        E[] newData = (E[])new Object[newCapacity + 1];
        for(int i = 0; i < size ; i++){
            newData[i] = data[(i + front) % data.length];
        }
        data = newData;
        front = 0;
        tail = size;
    }

    @Override
    public E dequeue() {

        if(isEmpty())
            throw new IllegalArgumentException("Cannot dequeue from an empty queue!");

        E ret = data[front];
        data[front] = null;
        front = (front + 1) % data.length;
        size--;

        if(size == getCapacity() / 4 && getCapacity() / 2 != 0)
            resize(getCapacity() / 2);

        return ret;
    }

    @Override
    public E getFront() {

        if(isEmpty())
            throw new IllegalArgumentException("Queue is empty!");
        return data[front];
    }
}
